1. Field of the Invention
The present invention relates to a medical diagnostic for investigating tissue components. More particularly, the present invention relates to an apparatus and a method that utilizes autofluorescence emission and/or polarized elastic light scattering as an interrogation means for investigating tissue states for medical applications.
2. Description of Related Art
Transplant surgeons often face the difficult question of whether organs from a cadaveric donor are suitable for transplantation. It is currently difficult to quantify how much warm ischemic organ damage has occurred, especially if a donor has experienced significant hemodynamic instability. Organ procurement in brain-dead and non-heart-beating donors can cause a variable amount of additional warm ischemia. Transplanting organs that have sustained significant pre-implantation warm ischemic damage may leave the recipient with unacceptably poor allograft function and adversely affect graft and patient survival. On the other hand, as transplant waiting lists continue to grow, it becomes increasingly important to maximize utilization of viable organs from marginal donors.
Post transplant monitoring is currently the only reliable way of assessing ischemic organ damage; unfortunately, at that stage the organ is already in the recipient and may have to be removed if found to be nonviable. Three fundamental questions regarding ischemia in a transplanted organ are apparent. First, how much ischemic damage has an organ sustained? Second, how does the organ respond to intervention aimed at halting or reversing ischemic damage? Third, how will the organ function after it is transplanted? Beneficial methods and apparatus for analyzing organ ischemia and answering such questions is needed at any stage of transplantation, while the organ is still in the donor, after it has been removed (during hypothermic preservation), while it is being implanted, and after reperfusion. Such methods and apparatus require real-time, substantially instantaneous results so that clinical decisions can be made in a timely fashion.
Background information on an existing approaches that addresses organ damage is described by Inman S., Osgood R., Plott W., et al., in “Identification of kidneys subjected to pre-retrieval warm ischemic injury during hypothermal perfusion preservation,” Transplant Proc., 1998, pp. 42-46, and in “The non heart-beating donor,” by Kootstra G., Kievet J K, Heineman E., Br Med Bull., (1997); 53 (4): 844, and in “Release of alpha-glutathione S-transferase (alpha GST) and pi-glutathione S-transferase (pi GST) from ischemic damaged kidneys into the machine perfusate-relevance to viability assessment,” Transplant Proc. (1997); 29 (8): 3591. However, such approaches are hindered by clinical practicality as well as by hypothermic preservation.
Background information on monitoring tissue viability is described and claimed in U.S. Pat. No. 2004/0054270 A1, entitled “Apparatus And Method For Monitoring Tissue Vitality Parameters,” issued Mar. 18, 2004 to Pewzner et al., including the following, “Apparatus for monitoring a plurality of tissue viability parameters of a tissue layer element, in which two different illumination sources are used via a common illumination element in contact with the tissue. One illumination source is used for monitoring blood flow rate and optionally flavoprotein concentration, and collection fibers are provided to receive the appropriate radiation from the tissue. The other illuminating radiation is used for monitoring any one of and preferably all of NADH, blood volume and blood oxygenation state of the tissue element, and collection fibers are provided to receive the appropriate radiation from the tissue.” However, such techniques from the above cited patent does not address detecting and quantifying ischemic tissue damage in its incipient stages in accordance with the principles of the present invention.
Accordingly, a need exists for methods and apparatus that can detect and quantify tissue parameters in its early stages before injury is clinically apparent and before irreversible damage has occurred. The present invention is directed to such a need.